Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed mice... more Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C12TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d approximately 30 nm. The spherical mixed micelles obtained upon addition of C12TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy.
ABSTRACT The triblock-copolymer system EO37-PO58-EO37 (P105)+o-xylene+water is found to organize ... more ABSTRACT The triblock-copolymer system EO37-PO58-EO37 (P105)+o-xylene+water is found to organize in a lamellar phase (Lα) upon addition of the surfactant C8TAB at constant oil-to-water ratio. Small-angle X-ray scattering (SAXS) is used to characterize the internal structure of the stacked bilayers and a detailed model of the structure (interlamellar spacing, bilayer thickness and composition of the amphiphilic film) is proposed on the basis of the SAXS data. Moreover, these data are used to investigate the elastic properties of the bilayers as a function of composition. It is shown that the excess area method and related concepts do not apply to the present system and it is not possible to give absolute values of the bending elastic constant κ. Nevertheless, it can be shown that the elasticity of the lamellar phase strongly decreases with increasing amount of surfactant, but is independent of the block-copolymer concentration. To our knowledge such information about the elastic properties of highly concentrated block-copolymer systems has not been presented in the literature before.
The invention relates to a novel composition for treating cancer, which allows the active substan... more The invention relates to a novel composition for treating cancer, which allows the active substance to be released in the direct presence of the cells which are to be treated with the active substance. Said composition comprises an active substance carrier which is in the form of a liposome comprising a disulfide group, a cytostatic agent being contained in the active substance carrier. The invention also relates to a method for the locally defined release of a cytostatic agent.
Materials Research Society Symposium Proceedings, 2012
ABSTRACT Creating optical quality thin films with a high refractive index is increasingly importa... more ABSTRACT Creating optical quality thin films with a high refractive index is increasingly important for waveguide sensor applications. In this study, we present optical models to measure the layer thickness, vertical and lateral homogeneity, the refractive index and the extinction coefficients of the polymer films with nanocrystal inclusions using spectroscopic ellipsometry. The optical properties can be determined in a broad wavelength range from 190 to 1700 nm. The sensitivity of spectroscopic ellipsometry allows a detailed characterization of the nanostructure of the layer, i.e. the surface roughness down to the nm scale, the interface properties, the optical density profile within the layer, and any other optical parameters that can be modeled in a proper and consistent way. In case of larger than about 50 nm particles even the particle size can be determined from the onset of depolarization due to light scattering. Besides the refractive index, the extinction coefficient, being a critical parameter for waveguiding layers, was also determined in a broad wavelength range. Using the above information from the ellipsometric models the preparation conditions can be identified. A range of samples were investigated including doctor bladed films using TiO2 nanoparticles.
The influence of the short alkyl-chain ionic surfactant OTAB on the dynamic behavior of an invers... more The influence of the short alkyl-chain ionic surfactant OTAB on the dynamic behavior of an inverse block copolymer-rich lamellar phase was investigated by neutron spin-echo spectroscopy (NSE). The observed intermediate scattering function can be described by a sum of two contributions. For high scattering vectors the model of Zilman-Granek plus a slow diffusional mode can be used to describe the experimental data and the bending elastic modulus κ for a polymer-rich membrane is calculated. At low scattering vectors the relaxation curves are strongly influenced by de Gennes narrowing arising from the structure factor of the Lα phase. Hence, the computed relaxation rates in this q-range are inversely proportional to the static structure factor. The present study demonstrates the necessity to directly investigate the dynamic behavior of lamellar phases and that an analysis of the width of the Bragg peaks can be insufficient to derive information about the single membrane elasticity, especially when both κ and B[combining macron] depend on the composition of the membrane.
ABSTRACT The micellar shape of Poly(butadiene)-b-poly(ethyleneoxide) (PB-PEO) plus Dodecyltrimeth... more ABSTRACT The micellar shape of Poly(butadiene)-b-poly(ethyleneoxide) (PB-PEO) plus Dodecyltrimethylammoniumbromide (DTAB) compound micelles was investigated by light scattering, small-angle X-ray scattering and small-angle neutron scattering in dependence of the molar ratio between block copolymer and surfactant. The given block copolymer forms cylindrical micelles in binary aqueous solution, which transform to spherical aggregates upon the addition of a sufficiently high amount of DTAB. It is interesting to note that the micellar shape seems to be a bistable feature, in the sense that it depends not only on the molar ratio of BCP and DTAB but also in a predictable manner on the preparation procedure of the solution.
The development of targeted and triggerable delivery systems is of high relevance for anticancer ... more The development of targeted and triggerable delivery systems is of high relevance for anticancer therapies. We report here on reduction-sensitive liposomes composed of a novel multifunctional lipidlike conjugate, containing a disulfide bond and a biotin moiety, and natural phospholipids. The incorporation of the disulfide conjugate into vesicles and the kinetics of their reduction were studied using dansyl-labeled conjugate 1 in using the dansyl fluorescence environmental sensitivity and the Förster resonance energy transfer from dansyl to rhodamine-labeled phospholipids. Cleavage of the disulfide bridge (e.g., by tris(2-carboxyethyl)phosphine (TCEP), dithiothreitol (DTT), l-cysteine, or glutathione (GSH)) removed the hydrophilic headgroup of the conjugate and thus changed the membrane organization leading to the release of entrapped molecules. Upon nonspecific uptake of vesicles by macrophages, calcein release from reduction-sensitive liposomes consisting of the disulfide conjugate and phospholipids was more efficient than from reduction-insensitive liposomes composed only of phospholipids. The binding of streptavidin to the conjugates did not interfere with either the subsequent reduction of the disulfide bond of the conjugate or the release of entrapped molecules. Breast cancer cell line BT-474, overexpressing the HER2 receptor, showed a high uptake of the reduction-sensitive doxorubicin-loaded liposomes functionalized with the biotin-tagged anti-HER2 antibody. The release of the entrapped cargo inside the cells was observed, implying the potential of using our system for active targeting and delivery.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006
ABSTRACT In emulsions, slippage due to wall depletion effects is well known in rheological invest... more ABSTRACT In emulsions, slippage due to wall depletion effects is well known in rheological investigations. This effect can be overcome by using geometries with serrated surfaces. However, we present here an easily practicable calculation that allows the slip data to be manipulated in order to determine the depletion layer thickness when data from both smooth and serrated surfaces is obtained. When studies are performed over a range of concentrations we show that there is a strong correlation between depletion layer thickness and emulsion composition. The experimental system used as the test case for the method was the ternary system triton X-100/water/tetradecane. Calculations were performed using data obtained for oil-in-water emulsions with the parallel plate geometry for a range of different gap sizes. The depletion layer thickness (≤1 μm) decreased on increasing the amount of dispersed phase, until at a sufficiently high concentration of dispersed phase (φmax = 0.73) slippage was no longer observed. The maximum depletion layer thickness was found to be a quadratic function of the relative volume fraction of the dispersed phase. The data coincide with those reported in the literature for a latex particle suspension if plotted using the same representation. Moreover, the proportionality constant was found to be of the order of the radius of the largest droplets in the dispersion. It is these droplets, which are chiefly responsible for the three-dimensional arrangement of the dispersed phase. This leads to the conclusion that the thickness of the depletion layer is controlled by the volume fraction and the size of the dispersed droplets.
ABSTRACT The development and accomplishments of encapsulation strategies in the agrochemical fiel... more ABSTRACT The development and accomplishments of encapsulation strategies in the agrochemical field are reviewed. To this end, reasons for the encapsulation of agrochemicals are given and put into context with the opportunities and risks for this kind of formulation. Practical examples of encapsulation are discussed with a focus on crop protection formulation, including a short overview of available technologies. In summary it can be concluded that the development of controlled release formulations of agrochemicals still lags somewhat behind earlier expectations, this being mainly due to the strongly varying and uncontrollable environmental conditions the capsules are applied in. Only very few products claiming a controlled release of the active have made it onto the market. However, new or greatly improved products can still be achieved by means of encapsulation in areas like overcoming acute toxicity, instability, and incompatibility of actives.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed mice... more Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C12TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d approximately 30 nm. The spherical mixed micelles obtained upon addition of C12TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy.
ABSTRACT The triblock-copolymer system EO37-PO58-EO37 (P105)+o-xylene+water is found to organize ... more ABSTRACT The triblock-copolymer system EO37-PO58-EO37 (P105)+o-xylene+water is found to organize in a lamellar phase (Lα) upon addition of the surfactant C8TAB at constant oil-to-water ratio. Small-angle X-ray scattering (SAXS) is used to characterize the internal structure of the stacked bilayers and a detailed model of the structure (interlamellar spacing, bilayer thickness and composition of the amphiphilic film) is proposed on the basis of the SAXS data. Moreover, these data are used to investigate the elastic properties of the bilayers as a function of composition. It is shown that the excess area method and related concepts do not apply to the present system and it is not possible to give absolute values of the bending elastic constant κ. Nevertheless, it can be shown that the elasticity of the lamellar phase strongly decreases with increasing amount of surfactant, but is independent of the block-copolymer concentration. To our knowledge such information about the elastic properties of highly concentrated block-copolymer systems has not been presented in the literature before.
The invention relates to a novel composition for treating cancer, which allows the active substan... more The invention relates to a novel composition for treating cancer, which allows the active substance to be released in the direct presence of the cells which are to be treated with the active substance. Said composition comprises an active substance carrier which is in the form of a liposome comprising a disulfide group, a cytostatic agent being contained in the active substance carrier. The invention also relates to a method for the locally defined release of a cytostatic agent.
Materials Research Society Symposium Proceedings, 2012
ABSTRACT Creating optical quality thin films with a high refractive index is increasingly importa... more ABSTRACT Creating optical quality thin films with a high refractive index is increasingly important for waveguide sensor applications. In this study, we present optical models to measure the layer thickness, vertical and lateral homogeneity, the refractive index and the extinction coefficients of the polymer films with nanocrystal inclusions using spectroscopic ellipsometry. The optical properties can be determined in a broad wavelength range from 190 to 1700 nm. The sensitivity of spectroscopic ellipsometry allows a detailed characterization of the nanostructure of the layer, i.e. the surface roughness down to the nm scale, the interface properties, the optical density profile within the layer, and any other optical parameters that can be modeled in a proper and consistent way. In case of larger than about 50 nm particles even the particle size can be determined from the onset of depolarization due to light scattering. Besides the refractive index, the extinction coefficient, being a critical parameter for waveguiding layers, was also determined in a broad wavelength range. Using the above information from the ellipsometric models the preparation conditions can be identified. A range of samples were investigated including doctor bladed films using TiO2 nanoparticles.
The influence of the short alkyl-chain ionic surfactant OTAB on the dynamic behavior of an invers... more The influence of the short alkyl-chain ionic surfactant OTAB on the dynamic behavior of an inverse block copolymer-rich lamellar phase was investigated by neutron spin-echo spectroscopy (NSE). The observed intermediate scattering function can be described by a sum of two contributions. For high scattering vectors the model of Zilman-Granek plus a slow diffusional mode can be used to describe the experimental data and the bending elastic modulus κ for a polymer-rich membrane is calculated. At low scattering vectors the relaxation curves are strongly influenced by de Gennes narrowing arising from the structure factor of the Lα phase. Hence, the computed relaxation rates in this q-range are inversely proportional to the static structure factor. The present study demonstrates the necessity to directly investigate the dynamic behavior of lamellar phases and that an analysis of the width of the Bragg peaks can be insufficient to derive information about the single membrane elasticity, especially when both κ and B[combining macron] depend on the composition of the membrane.
ABSTRACT The micellar shape of Poly(butadiene)-b-poly(ethyleneoxide) (PB-PEO) plus Dodecyltrimeth... more ABSTRACT The micellar shape of Poly(butadiene)-b-poly(ethyleneoxide) (PB-PEO) plus Dodecyltrimethylammoniumbromide (DTAB) compound micelles was investigated by light scattering, small-angle X-ray scattering and small-angle neutron scattering in dependence of the molar ratio between block copolymer and surfactant. The given block copolymer forms cylindrical micelles in binary aqueous solution, which transform to spherical aggregates upon the addition of a sufficiently high amount of DTAB. It is interesting to note that the micellar shape seems to be a bistable feature, in the sense that it depends not only on the molar ratio of BCP and DTAB but also in a predictable manner on the preparation procedure of the solution.
The development of targeted and triggerable delivery systems is of high relevance for anticancer ... more The development of targeted and triggerable delivery systems is of high relevance for anticancer therapies. We report here on reduction-sensitive liposomes composed of a novel multifunctional lipidlike conjugate, containing a disulfide bond and a biotin moiety, and natural phospholipids. The incorporation of the disulfide conjugate into vesicles and the kinetics of their reduction were studied using dansyl-labeled conjugate 1 in using the dansyl fluorescence environmental sensitivity and the Förster resonance energy transfer from dansyl to rhodamine-labeled phospholipids. Cleavage of the disulfide bridge (e.g., by tris(2-carboxyethyl)phosphine (TCEP), dithiothreitol (DTT), l-cysteine, or glutathione (GSH)) removed the hydrophilic headgroup of the conjugate and thus changed the membrane organization leading to the release of entrapped molecules. Upon nonspecific uptake of vesicles by macrophages, calcein release from reduction-sensitive liposomes consisting of the disulfide conjugate and phospholipids was more efficient than from reduction-insensitive liposomes composed only of phospholipids. The binding of streptavidin to the conjugates did not interfere with either the subsequent reduction of the disulfide bond of the conjugate or the release of entrapped molecules. Breast cancer cell line BT-474, overexpressing the HER2 receptor, showed a high uptake of the reduction-sensitive doxorubicin-loaded liposomes functionalized with the biotin-tagged anti-HER2 antibody. The release of the entrapped cargo inside the cells was observed, implying the potential of using our system for active targeting and delivery.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006
ABSTRACT In emulsions, slippage due to wall depletion effects is well known in rheological invest... more ABSTRACT In emulsions, slippage due to wall depletion effects is well known in rheological investigations. This effect can be overcome by using geometries with serrated surfaces. However, we present here an easily practicable calculation that allows the slip data to be manipulated in order to determine the depletion layer thickness when data from both smooth and serrated surfaces is obtained. When studies are performed over a range of concentrations we show that there is a strong correlation between depletion layer thickness and emulsion composition. The experimental system used as the test case for the method was the ternary system triton X-100/water/tetradecane. Calculations were performed using data obtained for oil-in-water emulsions with the parallel plate geometry for a range of different gap sizes. The depletion layer thickness (≤1 μm) decreased on increasing the amount of dispersed phase, until at a sufficiently high concentration of dispersed phase (φmax = 0.73) slippage was no longer observed. The maximum depletion layer thickness was found to be a quadratic function of the relative volume fraction of the dispersed phase. The data coincide with those reported in the literature for a latex particle suspension if plotted using the same representation. Moreover, the proportionality constant was found to be of the order of the radius of the largest droplets in the dispersion. It is these droplets, which are chiefly responsible for the three-dimensional arrangement of the dispersed phase. This leads to the conclusion that the thickness of the depletion layer is controlled by the volume fraction and the size of the dispersed droplets.
ABSTRACT The development and accomplishments of encapsulation strategies in the agrochemical fiel... more ABSTRACT The development and accomplishments of encapsulation strategies in the agrochemical field are reviewed. To this end, reasons for the encapsulation of agrochemicals are given and put into context with the opportunities and risks for this kind of formulation. Practical examples of encapsulation are discussed with a focus on crop protection formulation, including a short overview of available technologies. In summary it can be concluded that the development of controlled release formulations of agrochemicals still lags somewhat behind earlier expectations, this being mainly due to the strongly varying and uncontrollable environmental conditions the capsules are applied in. Only very few products claiming a controlled release of the active have made it onto the market. However, new or greatly improved products can still be achieved by means of encapsulation in areas like overcoming acute toxicity, instability, and incompatibility of actives.
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Papers by Holger Egger